NdFeB system sintered magnet
A NdFeB system sintered magnet according to the present invention is a NdFeB system sintered magnet having a base material produced by orienting powder of a NdFeB system alloy and sintering the powder, with Dy and/or Tb (the “Dy and/or Tb” is hereinafter called R H ) attached to and diffused from a surface of the base material through the grain boundary inside the base material by a grain boundary diffusion treatment, wherein the number of grain-boundary triple points at which the difference C t −C w between the R H content C t (wt %) at the grain-boundary triple point and the R H content C w (wt %) at a two-grain boundary portion leading to that grain-boundary triple point is equal to or smaller than 4 wt % is equal to or larger than 60% of the total number of grain-boundary triple points.
1. A NdFeB system sintered magnet having a base material produced by orienting powder of a NdFeB system alloy and sintering the powder, with Dy and/or Tb (R H ) attached to and diffused from a surface of the base material through a grain boundary inside the base material by a grain boundary diffusion treatment,
wherein a number of grain-boundary triple points at which a difference C t −C w between an R H content C t (wt %) at the grain-boundary triple point and an R H content C w (wt %) at a two-grain boundary portion is equal to or smaller than 4 wt % is equal to or larger than 60% of a total number of grain-boundary triple points, and
a percentage of a total volume of a carbon rich phase in a rare-earth rich phase at the grain-boundary triple points in the base material to a total volume of the rare-earth rich phase is equal to or lower than 50%.
2. The NdFeB system sintered magnet according to claim 1 , wherein a carbon content of the entire base material is equal to or lower than 1000 ppm.
3. The NdFeB system sintered magnet according to claim 2 , wherein an average grain size of main-phase grains which are grains constituting the base material is equal to or smaller than 4.5 μm.
4. The NdFeB system sintered magnet according to claim 1 , wherein an average grain size of main-phase grains which are grains constituting the base material is equal to or smaller than 4.5 μm.
5. The NdFeB system sintered magnet according to claim 1 , wherein the R H content decreases with an increase in the distance from the surface of the base material.